1. Field of the Invention
The present invention relates to a steerable front wheel suspension for a vehicle and, more particularly, to a front wheel suspension for a vehicle which can increase a free layout degree with respect to variation of a camber and caster, and improve handling safety by providing a nominal kingpin and decreasing variation of a height of roll-center by means of a nominal link, and then maximize the effective volume of an engine room by minimizing the space occupied by the suspension.
2. Description of Related Art
A conventional suspension for a vehicle connects an axle shaft and a car body to each other, and controls a position of a tire with respect to the car body for its optimal position during running of the vehicle. Thus, optimal handling safety may be obtained, and, the axle shaft is prevented from directly transmitting impact or vibration from a road surface to the car body, thereby preventing damage of baggage and improving riding comfort.
Particularly, in a steerable front wheel suspension, the suspension should be designed to absorb vibration or impact from the road surface as well as obtain running safety by maintaining an optimal position of a vehicle's straight ahead position and handling safety of a vehicle's turning point.
The front wheel is mounted to change its direction from right to left or from left to right, while centering the kingpin, and is also mounted with a geometric angle so as to meet the requisite for the front suspension.
Mounting the front wheel with the geometric angle is called a front wheel alignment. The front wheel alignment is distinguished by several elements, but the optimal operation of the front wheel is achieved by the supplemental operation of the elements with respect to each other. A kingpin inclination among the elements reduces a handling force of a steering wheel with a camber, absorbs an impact generated when the vehicle is running and being braked, and then increases restitution force of a steering wheel, thereby obtaining running safety in the vehicle's straight ahead position and handling safety in the vehicle's turning position.
The kingpin is mounted at an inclination such that its central line lies at a predetermined angle with respect to the vertical line when the vehicle is viewed from the front. An interval between the center line of the kingpin and a center line of the wheel is called offset. The offset is generally characterized as an offset at the wheel center and an offset at the ground. The offset at the wheel center has an effect on the vehicle's straight ahead running characteristics when either the driving force or the engine brake is applied to the wheels. The offset at the ground has an effect on the handling safety when the vehicle is braking or turning. If the offset at the ground is decreased, sensitivity with respect to the steering is decreased, such that the handling safety is increased when the vehicle is cornering and being braked.
Further, stability of the vehicle is closely related to the vibration of the car body. During the vehicle's running, rolling, pitching, and yawing occurs in addition to bounce. These vibrations should be absorbed to increase the stability and ride comfort of the vehicle.
In such vibrations, the rolling occurs at a predetermined point when the vehicle is in a turning situation, and this point is called a roll center. The variation rate of the roll center's height has an effect on the running safety and handling safety of the vehicle. Accordingly, to achieve running safety, it is more desirable to decrease the variation rate of the roll centert's height.
FIG. 6A is a front view of a conventional McPherson type (strut assembly type) suspension. This suspension includes a strut assembly 73 having a shock absorber 72 and being integrally formed with a knuckle 71, a lower arm 75 and a ball joint 76.
This suspension has an advantage in its simple structure and weight. To reduce the kingpin offset a or attain a negative (-) state, the knuckle 71 of the strut assembly 73 must be moved to the engine room, or the ball joint 76 must be moved to an outside of the engine room. However, in the case where the knuckle 71 is moved to the engine room, the available volume of the engine room is to be reduced simultaneously with increasing a kingpin angle thereby having a bad effect on the cornering performance of the vehicle. Also, it is impossible to move the ball joint portion 76 outside of the engine room because of being interfered with by a disk brake. Therefore, this suspension has a problem in reducing the kingpin offset.
FIG. 6B is a front view of conventional Wishbone type (strut assembly type) suspension, wherein the suspension includes upper and lower control arms 81, 82; a steering knuckle 83; a strut assembly 85 having a shock absorber 84 and a spring; and ball joints 86, 87 of the upper and lower control arms 81, 82. A kingpin offset may be reduced by moving a car body-side connecting portion 88 of the upper control arm 81 to the engine room and moving the ball joint 87 of the lower control arm 82 to the outside, even though this suspension has an advantage in its simple structure and weight. To reduce the kingpin offset or attain a negative (-) state, when the car body-side connecting point 88 of the upper control arm 81 is moved to the engine room, the available volume of the engine room is reduced simultaneously with increasing the kingpin offset a. The cornering performance of the vehicle may be adversely affected thereby. And also, it is impossible to move the ball joint 87 of the lower control arm 82 outwardly because of interference with a disk brake. Therefore, this suspension has problems in reducing the kingpin offset.
Further, if the length of the upper control arm is shortened, the kingpin offset may be almost zero, with an increased bushing effect and change in the camber angle. On the contrary, if the length of the upper control arm becomes long, the bushing effect can be decreased but the change in the camber angle and kingpin offset cannot be reduced to zero.
That is, the above conventional suspension systems cannot solve the combined problems of the kingpin offset, steering angle, and bushing effect at the same time.
Accordingly, there is a limit to a free layout degree with respect to providing an angle of a kingpin not to reduce the size of the kingpin offset.
In both the systems the wheels rotate upward and downward depending on the control arms having short lengths, and the height of roll-center is greatly changed thereby adversely affecting driving safety.
Therefore, the present invention has been made in an effort to solve the above-described problems of the conventional front suspension.